Since the inception of engine-propelled vehicles it has been necessary to transfer power from the engine to at least one (1) drive wheel. While many schemes have been implemented to transfer power one highly successful approach is to couple the engine output to a transmission and from the transmission to a drive shaft and from the drive shaft to a transaxle and from the transaxle to one (1) or more wheels.
The foregoing drive train has at least one (1) major problem when used in modern vehicles. Modern vehicles have suspension systems that provide comfort, stability, and improved handling characteristics. Such suspension systems require the drive train to operate over varying angles between the transmission and the transaxle. Since straight-line drive trains are unsuitable some means of handling varying drive train angles is required.
One (1) very successful approach to handling varying drive train angles is to insert a “U” joint between the transmission and the transaxle. While “U” joints are remarkably strong and allow varying drive train angles, in practice the angle ranges are limited. As the angle gets too great “U” joints become difficult to turn and “notchy” in that smooth rotation is lost.
When the range of drive train angles becomes too great, such as in modern front wheel drives systems, “U” joints become ineffective. Modern front wheel drive systems can and do develop drive train angles that “U” joints just cannot properly handle. Because of that modern front wheel drive systems replace “U” joints with coupling joints that can handle much large drive train angles.
Coupling joints transfer power in such a manner that the rotational velocity between the power drive side and the output drive side remain constant. In “U” joints, the rotational velocity varies over a complete rotation. The greater the drive train angle the larger the rotational velocity varies.
While many different implementations of coupling joints have been developed over the years as a general rule coupling joints have various problems that “U” joints typically don't suffer from. Coupling joints are usually not as strong as “U” joints, they suffer from a high sensitivity to contamination, they have numerous components parts, they are heavy and rather difficult to assemble and difficult to install, and they can be very difficult and expensive to lubricate.
Accordingly, there exists a need for relatively strong coupling joints that are relatively insensitive to contamination, have fewer components and are thus lighter, and are easy to assemble, install and lubricate.